1. Field of the Invention
The present invention relates to an abrasive grain to carry out finish machining of hard and fragile materials, such as silicon, glass and so on, and a metal material, for example, steel, aluminum and so on, and further to a method for producing the abrasive grain, a polishing tool composing of the abrasive grain and having a long operation life, a polishing apparatus which has the polishing tool and a method for producing the polishing tool, which contributes to a high quality and a high efficiency of a processing.
2. Description of the Prior Art
For a final finishing of a part, which is made of a silicon wafer, a glass disk, various hard and fragile materials, or metal materials, a polishing process using a loose-abrasive slurry has been widely adopted because this process is easy to use a fine abrasive grain so that a fine finishing surface can be obtained easily. Moreover, a large amount of abrasive slurry can also maintain stable processing characteristics of the final finishing by means of a stable supplying of the slurry.
However, this polishing processing, which uses the abrasive slurry, requires a large amount of slurry, and discharges a waste of the large amount of slurry, so that it has a great impact on environment conservation.
This polishing processing has also a limit for increasing a processing efficiency. Under such circumstances, a development of a fixed-abrasive processing tool, which can produce an excellent finishing surface more than the similar to that obtained by using the loose-abrasive slurry, is actively carried out in various fields.
For a finishing process with abrasive grain, it is an advantageous to use a fine abrasive grain in order to produce an excellent surface roughness, which is also normally true for the fixed-abrasive processing tool.
However, in order to produce an excellent surface such as a mirror surface, a contact between a bonding material bonding the abrasive grain and a backing and a work piece is caused by using the fixed-abrasive processing tool in which a particle diameter is less than several μm, and also chips of the bonding material and the abrasive grains are accumulated among the abrasives grains, and then clogging of the abrasive grains are caused.
As a result, not only the removal rate would be decreased, but also the surface quality would be damaged, and in a worst case, it is not possible to carry out the finishing process of the work piece by the abrasive grains.
Moreover, even though a method for controlling the contact between the bonding material of abrasive grains and the work piece is taken, there is a problem for declining processing efficiency because a diameter of each of the abrasive grains is small.
On the other hand, when an abrasive grain in which a diameter of a particle is large is selected to use, it is possible to improve the processing efficiency, but the quality of the surface is deteriorated, and it tends to be difficult to produce the mirror surface.
In order to solve these problems, the abrasive grain is powdered and then the powder is agglomerated and the fixed-abrasive processing tool, which uses the agglomerated powder as the abrasive grain is proposed. (References: Japanese Patent Laid-Open Hei7-164324, Hei8-155840, 2000-198073, 2000-237962, 2000-176842, and 2001-129764, Japanese Patent publication Hei9-504235)
For this fixed-abrasive grain processing tool, the excellent surface roughness is provided by an action of the fine abrasive grain, and at the same time, an improvement of the processing efficiency by the agglomerated abrasive grain can be accomplished.
However, it is still required that further improvements in the processing efficiency and the processing life should be achieved. Moreover, these proposed technologies do not focus on a bonding strength among the fine particles comprising the abrasive grain, so that requirements of improving the processing efficiency can hardly be met.